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Action under the Montreal Protocol has contributed to climate change mitigation for almost 35 years. The phase-out of ozone-depleting substances (ODS) has set the ozone layer on a path to recovery, protecting the world's biosphere from harmful ultraviolet radiation. The 2016 Kigali Amendment to the Montreal Protocol is expected to avoid 5.6–8.7 gigatonnes of carbon-dioxide equivalent (GtCO2e) emissions of hydrofluorocarbons (HFC) per year by 2100, reducing the impact of HFCs on global average warming by up to 0.4°C. Despite its successes, unexpected emissions of phased out ODS – notably the chlorofluorocarbon, CFC-11 - have brought attention to shortcomings in the Protocol's monitoring, reporting, verification and enforcement (MRV+E) which must be addressed to guarantee its controls are sustained. Meanwhile, additional significant mitigation could be achieved by accelerating the phase-down of HFCs under the Kigali Amendment, by tackling ODS and HFC emissions from leaking banks of equipment and products and by controlling feedstocks, which are not subject to Montreal Protocol phase-out controls. Recent scientific papers have linked almost 870 million tCO2 per year of greenhouse gases (GHG) and ODS to fluorochemical industrial processes and illegal fluorochemical production. Expanding the scope of the Montreal Protocol to address nitrous oxide (N2O), itself an ODS and GHG, would also contribute substantial ozone and climate benefits. This perspective essay discusses new and strengthened policy measures that governments can consider under the Montreal Protocol in order to maximize early, cost-effective reductions in emissions of non-CO2 greenhouse gases and ensure future implementation. Highlights: Perspective essay examining non-CO2 emission reductions under the Montreal Protocol. Significant ongoing emissions are linked to unregulated fluorochemical production. Strengthened institutions and processes will avoid illegal trade and sustain compliance. Addressing ODS and HFC banks and N2O emissions present additional opportunities. The global HFC phase-down must be accelerated to meet the 1.5°C climate goal. [ABSTRACT FROM AUTHOR]

We present an efficient, general-purpose variant of the Widom test particle insertion method for computing chemical potentials of gaseous solutes in fluids or porous solids. The method is implemented in the Monte Carlo molecular simulation engine Cassandra, but receiving phase configurations are independent of this process and may be pre-sampled by other molecular simulation engines such as molecular dynamics codes. Efficiency enhancements present in this method include configurational biasing and accelerated atomic overlap detection. When applied to the estimation of Henry's law constants of atomistic difluoromethane and pentafluoroethane in ionic liquids, the accelerated overlap detection results in a speedup of more than an order of magnitude compared to conventional methods without sacrificing accuracy. We found good agreement between this method and Hamiltonian replica exchange (HREX) for Henry's law constant and absorption isotherm estimation. This embarrassingly parallel method is especially well suited for screening Henry's law constants of many small gases in the same solvents, since a liquid trajectory can be reused for as many solutes as desired. [ABSTRACT FROM AUTHOR]

A kinetic model is presented for high-temperature oxidation and combustion of the refrigerants: 2,3,3,3-tetrafluoropropene (R-1234yf), 1,3,3,3-tetrafluoropropene (R-1234ze(E)), and 3,3,3-trifluoropropene (R-1243zf) at atmospheric pressure. The kinetic model is based on: GRI-Mech-3.0 and previously developed models for the inhibition of hydrocarbon flames by 2-bromo-3,3,3-trifluoropropene (2-BTP) and C1-C2 hydrofluorocarbons. The model includes 1001 reactions and 105 species. Thermodynamic equilibrium calculations indicate a maximum combustion temperature of 2047 K, 2037 K, and 2312 K for R-1234yf, R-1234ze(E), and R-1243zf, respectively, in air for standard conditions. Calculations of the 1D, steady, adiabatic, laminar burning velocity for these refrigerants with air or oxygen-enriched air indicate reasonable agreement with experimental data from the literature when the burning velocity is above 10 cm/s. The simulations are used to understand the relevant reactions. Despite the relatively high F/H ratio in the reactants (2), the combustion is dominated by reactions with radical pool radicals typical of hydrocarbons (O, OH, and H). The combustion of R-1234yf or R-1234ze(E) is characterized by a two-zone flame, the second of which is a slow reaction zone accounting for CO and CF2O consumption and additional temperature rise of a few hundred K. Simulations of the effects of water vapor on the burning velocity of R-1234yf and R-1234ze(E) capture qualitatively the trends in the experimental results. For certain values of the equivalence ratio and oxygen content of air, the premixed flame structure shows temperature peak in the main reaction zone higher than the equilibrium value. [ABSTRACT FROM AUTHOR]

Pool boiling heat transfer performance of hydro-fluorocarbon refrigerant R-134a on titanium dioxide (TiO2) nanoparticle coated surface is experimentally studied in the article. The test surfaces, viz, 100 nm, 200 nm and 300 nm thick TiO2 nanoparticle coated surfaces over 100 nm thin film surface are used in this experimentation. The surfaces are synthesized and fabricated by simple and cost-effective electron beam evaporation method. The test surfaces were characterized by scanning electron microscope and atomic force microscope to uncover the formation of crystalline structure on coated surfaces. These surfaces are utilized in pool boiling test rig using refrigerant R134a at 10°C saturation temperatures. The result indicated that a maximum of 87.5% augmentation in the boiling heat transfer has been achieved by higher thickness of TiO2 coated surface than the bare copper surface. In addition, the incipience wall superheat is reduced for higher thickness coated surface. The augmentation of heat transfer coefficient might be the reason for increase in micro/nano-porosity, active nucleation site density and surface area of the heating surface. It is observed that with the increase of sub-cooling temperature of liquid, the bubble departure diameter was reduced while the heat transfer coefficient has been increased. [ABSTRACT FROM AUTHOR]

The global and long-term nature of climate change conflicts with the self-interest and short-term dominated priorities of decision-makers. Climate change mitigation makes sense at the global level, but not at the level of the individual decision-maker. This conflict has been and remains the main obstacle to effective global cooperation and mitigation. This paper proposes a framework that aligns climate action with short-term self-interest through results-based payments to governments. Its key components are: determining an emission benchmark for each country as well as a price for carbon saving; paying countries annually for reducing emissions below their respective benchmark; a new international fund to finance these annual payments by borrowing capital from private investors; and repaying borrowings in the long-term through payments made by countries to the fund based on a predetermined allocation mechanism. This framework would offer important benefits over an approach focused on allocating climate action or a carbon budget among countries. These include the improved prospect of reaching an effective climate agreement and delivering fast and dramatic mitigation thanks to stronger political commitment, the transformation of short-term self-interest from an obstacle into a driver of climate action, and the additional financing created. The paper also proposes a pilot scheme focusing on hydrofluorocarbon emissions with a considerably lower financing requirement. This offers the possibility of an alternative financing mechanism, and thus a faster and more straightforward implementation path. Short-term financial incentives offered to governments could turn policy action from a burden into an opportunity from their perspective unlocking a huge potential for timely mitigation. [ABSTRACT FROM AUTHOR]

Chlorofluorocarbons (CFCs) were introduced in the 1930s as the safe replacements for the toxic and flammable refrigerants being used at that time. Subsequently, hydrochlorofluorocarbons (HCFCs) were also developed. In addition to refrigerant applications, they were used as foam blowing agents, as solvents and as propellants for many aerosols. In the 1970s and 1980s, concern developed about their environmental impact, specifically on stratospheric ozone depletion. Industry began to consider acceptable replacements. In 1987, many of the governments of the world came together and drafted the Montreal Protocol, calling upon Industry to initially phase out production of the CFCs and later HCFCs. Within 4months of the signing of the Montreal Protocol, the 15 global major producers joined together to form the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS), which sponsored research into environmental effects and the Program for Alternative Fluorocarbons toxicity Testing, PAFT), which examined the toxicology of potential replacements for the CFCs and HCFCs. Nine replacements were identified by companies and, through this international cooperation; toxicology programs were designed, conducted, and evaluated without duplication of effort and testing; consequently these new products were introduced within less than 10 years. Indeed the Montreal Protocol has been recognized as the most appropriate international treaty to phase-down HFCs. In 2016 the Kigali Amendment to the Montreal Protocol set out a phase-down schedule for the consumption and production of HFCs. In order to reduce the consumption and emissions of high GWP HFCs. Recently lower GWP HFCs and very low GWP HFOs (hydrofluoroolefins and HCFOs (hydrochlorofluoroolefins) have been introduced into a range of applications. Summaries of the toxicology profiles of some of the original CFCs and HCFCs, the replacements and the new post-PAFT replacements are described. The chemicals in this review include CFC-11, CFC-12, CFC-113, CFC-114, HCFC 22, HCFC-123, HCFC-124, HCFC-141b, HCFC-142b, HCF-32, HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-245ea, HFC-245fa, HFO-1234yf, HFO-1234ze, and HCFO-1233zd. [ABSTRACT FROM AUTHOR]

Experimental studies of particle formation from solution droplets were conducted using a newly developed monodisperse spray drying process. Solutes beclomethasone dipropionate and caffeine were dissolved in ethanol, pressurized hydrofluoroalkane propellant 134a, and mixtures thereof. Solutions were atomized into monodisperse microdroplets using a custom droplet generator installed in a laboratory scale spray dryer, enabling drying and collection of the resulting monodisperse microparticles. The effects of droplet diameter, solution concentration, solvent composition, and drying rate on the physical properties of the dried particles were evaluated. Particle morphology and size were assessed using ultramicroscopy and image analysis of micrographs. Extent of crystallinity and polymorphism were investigated using Raman spectroscopy. The drying temperature was found to have a large effect on the morphology of amorphous beclomethasone dipropionate particles. Particles dried near room temperature were spheroidal to ellipsoidal with prevalent surface concavities and evidence of shell buckling; increasing the drying temperature for fixed droplet size and composition resulted in a transition to more spherical, smooth-surfaced particle morphologies. Crystalline caffeine microparticles were made up of assemblies of multiple crystallites. The measured length and breadth of these crystallites was found to be correlated with the time available for crystal nucleation and growth as calculated using a particle formation model. The results highlight the abilities and limitations of currently available particle formation models in elucidating the relationships between the size, composition, and evaporation rate of drying solution droplets and the physical properties of the resulting particles. The work demonstrates the suitability of monodisperse spray drying as an experimental technique for investigating the fundamentals of particle formation from solution droplets. © 2018 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Evaporators of small and medium refrigeration systems, as in commercial and automobile air conditioning applications, are being studied to develop more compact and lighter equipment, that reaches good thermal performance and reliability, with low pressure drop. In this way, evaporators are being designed with small channels and materials like aluminum. Moreover, different refrigerants are being tested to substitute for hydrofluorocarbon (HFC) refrigerants, with different operational temperatures and pressures. Some of them, like hydrocarbons, although they present advantages with respect to their thermodynamic and transport properties, should be used with small charge in the system due to their flammability. This work presents the results of an experimental study to characterize the flow boiling of the refrigerant R600a (isobutane) in a multiport aluminum extruded tube with 7 parallel minichannels of 1.47 mm hydraulic diameter. The effects of mass velocity, heat flux, and vapor quality on heat transfer were investigated for constant saturation temperature and pressure. Heat fluxes in the range from 5 to 30 kW m−2, mass velocities set to discrete values in the range of 50 to 200 kg m−2s−1, and saturation temperature of 20°C were considered. It was verified a significant effect of heat flux. Moreover, some images of flow patterns, in different conditions, are presented, and the main patterns identified were slug, intermittent, and annular. [ABSTRACT FROM AUTHOR]

Prospects for policy and regulatory actions to reduce, restrict, and even eliminate the use of today's hydrofluorocarbon refrigerants continue to exist and grow because of their relatively high global warming potentials and consequent impact on climate. These regulatory actions are leading to the development and investigation of a new class of refrigerants, unsaturated chlorinated and fluorinated hydrocarbons, with lower global warming potentials. Tradeoffs between global warming potential, flammability, and specific capacity will need to be made and these tradeoffs may result in the need for changes to equipment designs. Some lower global warming potential refrigerants are beginning to be introduced in many market segments. This article provides an overview of the next generation refrigerants available or under development and presents the state of understanding and development of these alternatives by their environmental, safety, and design tradeoffs. [ABSTRACT FROM AUTHOR]

Trifluoroacetic acid (TFA) is a breakdown product of several hydrochlorofluorocarbons (HCFC), regulated under the Montreal Protocol (MP), and hydrofluorocarbons (HFC) used mainly as refrigerants. Trifluoroacetic acid is (1) produced naturally and synthetically, (2) used in the chemical industry, and (3) a potential environmental breakdown product of a large number (>1 million) chemicals, including pharmaceuticals, pesticides, and polymers. The contribution of these chemicals to global amounts of TFA is uncertain, in contrast to that from HCFC and HFC regulated under the MP. TFA salts are stable in the environment and accumulate in terminal sinks such as playas, salt lakes, and oceans, where the only process for loss of water is evaporation. Total contribution to existing amounts of TFA in the oceans as a result of the continued use of HCFCs, HFCs, and hydrofluoroolefines (HFOs) up to 2050 is estimated to be a small fraction (<7.5%) of the approximately 0.2 μg acid equivalents/L estimated to be present at the start of the millennium. As an acid or as a salt TFA is low to moderately toxic to a range of organisms. Based on current projections of future use of HCFCs and HFCs, the amount of TFA formed in the troposphere from substances regulated under the MP is too small to be a risk to the health of humans and environment. However, the formation of TFA derived from degradation of HCFC and HFC warrants continued attention, in part because of a long environmental lifetime and due many other potential but highly uncertain sources. [ABSTRACT FROM AUTHOR]

Attention Restoration Theory (ART) suggests the ability to concentrate may be restored by exposure to natural environments. Although widely cited, it is unclear as to the quantity of empirical evidence that supports this. A systematic review regarding the impact of exposure to natural environments on attention was conducted. Seven electronic databases were searched. Studies were included if (1) they were natural experiments, randomized investigations, or recorded “before and after” measurements; (2) compared natural and nonnatural/other settings; and (3) used objective measures of attention. Screening of articles for inclusion, data extraction, and quality appraisal were performed by one reviewer and checked by another. Where possible, random effects meta-analysis was used to pool effect sizes. Thirty-one studies were included. Meta-analyses provided some support for ART, with significant positive effects of exposure to natural environments for three measures (Digit Span Forward, Digit Span Backward, and Trail Making Test B). The remaining 10 meta-analyses did not show marked beneficial effects. Meta-analysis was limited by small numbers of investigations, small samples, heterogeneity in reporting of study quality indicators, and heterogeneity of outcomes. This review highlights the diversity of evidence around ART in terms of populations, study design, and outcomes. There is uncertainty regarding which aspects of attention may be affected by exposure to natural environments. [ABSTRACT FROM AUTHOR]

India's growing role in the global climate debate makes it imperative to analyse emission reduction policies and strategies across a range of GHGs, especially for under-researched non-CO2gases. Hydrofluorocarbons' (HFCs) usage in cooling equipment and subsequent emissions are expected to increase dramatically in India with the phase-out of hydrochlorofluorocarbons (HCFCs) as coolants in air-conditioning equipment. We focus on the residential air-conditioning sector in India and analyse a suite of HFC and alternative coolant gas scenarios for understanding the implications for GHG emissions from this sector within an integrated assessment modelling framework. We find that, if unabated, HFC410A emissions will contribute to 36% of the total global warming impact from the residential air-conditioner sector in India in 2050, irrespective of the future economic growth trajectory, and the remaining 64% is from energy to power residential air-conditioners. A move towards more efficient, low global warming potential (GWP) alternative refrigerants will significantly reduce the cumulative global warming footprint of this sector by 37% during the period 2010–2050, due to gains both from energy efficiency as well as low GWP alternatives. Best practices for reducing direct emissions are important, but only of limited utility, and if a sustainable lifestyle is adopted by consumers with lower floorspace, low GWP refrigerants, and higher building envelope efficiencies, cumulative emissions during 2010–2050 can be reduced by 46% compared to the Reference scenario. Policy relevance Our analysis has important implications for Indian climate policy. We highlight that the Indian government's amendment proposal to the Montreal Protocol is a strong signal to the Indian market that the transition away from high GWP refrigerants towards low/zero GWP alternatives will happen sooner or later. The Bureau of Energy Efficiency should extend building energy conservation code policy to residential buildings immediately, and the government should mandate it. Government authorities should set guidelines and mandate reporting of data related to air-conditioner coolant recharge frequency and recovery of scrapped air-conditioner units. For contentious issues like flammability where there is no consensus within the industry, the government needs to undertake an independent technical assessment that can provide unbiased and reliable information to the market. [ABSTRACT FROM PUBLISHER]

Greenhouse gases (GHGs) other than carbon dioxide (CO2) play an important role in the effort to understand and address global climate change. Approximately 25% of Global warming potential-weighted GHG emissions in the year 2005 comprise the non-CO2GHGs. The report,Global Mitigation of Non-CO2Greenhouse Gases: 2010–2030provides a comprehensive global analysis and resulting data-set of marginal abatement cost curves that illustrate the abatement potential of non-CO2GHGs by sector and by region. The basic methodology – a bottom-up, engineering cost approach – builds on the baseline non-CO2emissions projections published by EPA, applying abatement options to the emissions baseline in each sector. The results of the analysis are MAC curves that reflect aggregated breakeven prices for implementing abatement options in a given sector and region. Among the key findings of the report is that significant, cost-effective abatement exists from non-CO2sources with abatement options that are available today. Without a price signal (i.e. at $0/tCO2e), the global abatement potential is greater than 1800 million metric tons of CO2equivalent. Globally, the energy and agriculture sectors have the greatest potential for abatement. Among the non-CO2GHGs, methane has the largest abatement potential. Despite the potential for project level cost savings and environmental benefits, barriers to mitigating non-CO2emissions continue to exist. This paper will provide an overview of the methods and key findings of the report. [ABSTRACT FROM AUTHOR]

The article presents comments on several articles related to the issues of air quality and climate change. Professor Michael T. Kleinman discusses hydrofluorocarbons and the health aspects of multiple air pollutants that contribute to fine particles and ozone. Howard J. Feldman tackles the link between climate change and pollutant buildup. J. Jason West elaborates on the interconnections between air pollution and climate change.

Hydrofluorocarbons have been used as replacement gases of chlorofluorocarbons, since the latter have been phased out by the Montreal Protocol due to their environmental hazardous ozone-depleting effects. This is also the case of difluoromethane (CH2F2, HFC-32), which nowadays is widely used in refrigerant mixtures together with CF3CH3, CF3CH2F, and CF3CHF2. Due to its commercial use, in the last years, the atmospheric concentration of HFC-32 has increased significantly. However, this molecule presents strong absorptions within the 8–12 μm atmospheric window, and hence it is a greenhouse gas which contributes to global warming. Although over the years several experimental and theoretical investigations dealt with the spectroscopic properties of CH2F2, up to now pressure broadening coefficients have never been determined. In the present work, the line-by-line parameters of CH2F2are retrieved for either ground state or ν7band transitions by means of microwave (MW) and infrared (IR) absorption spectroscopy, respectively. In particular, laboratory experiments are carried out on 9 pure rotational transitions of the ground state and 26 ro-vibrational transitions belonging to the ν7band lying around 8.2 μm within the atmospheric region. Measurements are carried out at room temperature on self-perturbed CH2F2as well as on CH2F2perturbed by N2and O2. The line shape analysis leads to the first determination of self-, N2-, O2-, and air-broadening coefficients, and also of line intensities (IR). Upon comparison, broadening coefficients of ground state transitions are larger than those of the ν7band, and no clear dependence on the rotational quantum numbers can be reported. The obtained results represent basic information for the atmospheric modelling of this compound as well as for remote sensing applications. [ABSTRACT FROM PUBLISHER]

The present article provides preliminary results about the environmental Kuznets curve (EKC) hypothesis in the Italian case for some less investigated air contaminants, such as benzene, sulphur hexafluoride and hydrofluorocarbons (HFCs). By using an emission data set disaggregated at the provincial level, it investigates whether the EKC is influenced by the geographical dimension, by splitting the national sample into four provincial subsets, according to the characteristics of the Italian productive system. Results suggest that southern provinces follow an EKC for the benzene and sulphur hexafluoride emissions, along with north-eastern provinces that follow a U-shaped trend for HFCs, thus providing evidence that geographical dimension significantly influences the relationship between income and pollutant emissions. [ABSTRACT FROM PUBLISHER]

□ Adsorption properties (enthalpy of adsorption, entropy of adsorption, and free energy of adsorption) of several hydrofluorocarbons (HFCs) on natural and surfactants modified clay minerals (bentonites, rectorite clays, and activated clays) were evaluated over the temperature range of 40–100°C by inverse gas chromatography. The differences of thermodynamic parameters of HFCs on different clay minerals mainly depended on the surface polarity and the interlayer spacing of clay mineral. When the clay minerals were modified by surfactants, such as cetyltrimethylammonium bromide, sodiumdodecyl benzene sulfonate, and tetrabutyl ammonium bromide, the adsorption values for the HFCs were weaker. However, the free energies of adsorption on natural and modified clay mineral were negative, implying the adsorptive processes of HFCs on clay were spontaneous at these temperatures. These results may have implications to reduce the atmospheric lifetimes of HFCs. [ABSTRACT FROM AUTHOR]

High yield and selectivity in the intramolecular synthesis of the macrocyclic lactone oxacyclohexadecan-2-one were achieved via a straightforward biocatalytic synthesis utilising non-conventional solvents: supercritical carbon dioxide (scCO2), ethane, fluoroform and 1,1,1,2-tetrafluoroethane. Batch and continuous syntheses were demonstrated with a higher yield attained in a continuous synthesis using in-situ product extraction by scCO2. A remarkably high yield was obtained in 1,1,1,2-tetrafluoroethane at batch conditions. [ABSTRACT FROM AUTHOR]

This article considers the heat transfer and pressure drop performance potentials of halogenated propene isomers during in-tube condensation and in-tube flow boiling using the penalty factor and total temperature penalization concepts, respectively. In particular, five isomers are considered: R-1233xf, R-1233zd(E), R-1234yf, R-1234ze(E), and R-1243zf. In addition, to these five pure fluids, the heat transfer and pressure drop performance potentials are investigated for five R-32/R-1234yf blends and for twenty-seven blends being considered as part of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) Low-GWP Alternative Refrigerants Evaluation Program. The article also presents thermophysical property estimations for the five pure fluids relative to R-134a or R-123, and the five R-32/R-1234yf blends relative to R-134a. The thermophysical properties considered are the ones that influence the heat transfer and pressure drop performance potentials, and include the thermodynamic properties temperature, pressure, density, latent heat of vaporization, and specific heat, and the transport properties thermal conductivity and viscosity. The article also presents a literature review of relevant articles for condensation and boiling heat transfer and pressure drop of fluorinated propene isomers. [ABSTRACT FROM AUTHOR]

Trans-1-chloro,3,3,3-trifluoropropene (HCFO-1233zd(E)) is being developed as a foam blowing agent, refrigerant and solvent because it has a very low global warming potential (<10), as contrasted to the hydrofluorocarbons (>500). The toxicology profile is described. The acute 4-hour 50% lethal concentration value in rats receiving HCFO-1233zd(E) was 120 000 ppm. The no observed effect level (NOEL) in cardiac sensitization studies in dogs was 25 000 ppm. In a 2-week range-finding study, rats were exposed to HCFO-1233zd(E) at levels of 0, 2000, 7500 and 20 000 ppm 6 hours/day for 5 days/week. Histopathological changes in the heart described as multifocal mononuclear infiltrates were observed in males (mid- and high-exposure group) and females (high-exposure group), suggesting this organ was the target for HCFO-1233zd(E) toxicity. In a 4-week study, rats were exposed to 0, 2000, 4500, 7500 and 10 000 ppm. The only finding was an increase in potassium (mid- and high-exposure males). No increase was observed after a 2-week recovery period, nor in a subsequent 13-week toxicity study. In a 13-week study, rats were exposed to 4000, 10 000 and 15 000 ppm 6 hours/day for 5 days/week. Findings consisted of multifocal mononuclear cell infiltrates in the heart with a NOEL/lowest observed adverse effect level of 4000 ppm. No genetic toxicity was observed in a battery of genetic toxicity studies. In a rat prenatal developmental toxicity study, dilated bladders were observed in the high-exposure group fetuses (15 000 ppm), a finding of unclear significance. HCFO-1233zd(E) was not a developmental toxin in rabbits, even at exposure levels up to 15 000 ppm. [ABSTRACT FROM AUTHOR]

Due to growing concerns over anthropogenic effects on the climate, there is increasing need to replace engineered fluids of high global warming potentials (GWPs), such as hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs), with more environmentally friendly alternatives in thermal management systems. This article presents experimental data and compares various correlations for predicting the pool boiling heat transfer coefficient of a new low-GWP fluid, FK-649. Using a pressurized boiling facility with a smooth aluminum heater, the critical heat flux (CHF) and heat transfer coefficient were measured for the pool boiling of FK-649 at various saturation conditions. The commonly used refrigerant tetrafluoroethane (R-134a) is tested in the same pressurized facility to act as a benchmark for the new fluid. While R-134a exhibited a higher heat transfer coefficient and CHF, this behavior is expected from the fluid properties. Two-phase heat transfer performance of FK-649 is expected to be similar to that of the fluorocarbon FC-72. Experimental data are compared to predictions using the Rohsenow, Borishanskii–Mostinski, Stephan and Abdelsalam, Cooper, and Leiner correlations. Where applicable, empirical constants are obtained by using a least-squares fit to experimental data. The Rohsenow correlation yielded the best result with a new surface–fluid constant Cs,f of 0.0037 for FK-649. [ABSTRACT FROM AUTHOR]

The performance of XP10, a new refrigerant with a reduced global warming potential, in a centrifugal chiller designed for HFC-134a with a cooling capacity of 1969.44 kW (560 tons) was measured under full- and part-load conditions and compared to performance with HFC-134a. Measured chiller energy efficiencies with XP10 were comparable to those with HFC-134a. They resulted in 0.6% higher energy consumption for XP10 when integrated over a representative profile of partial loads as described by AHRI Standard 550/590 (AHRI 2003). Based on the measured chiller performance, XP10 could be considered a near drop-in replacement for HFC-134a in centrifugal chillers. It could replace HFC-134a in existing chillers or enable optimized new chiller designs without extensive equipment and no flammability code modifications. The total equivalent warming impact of a chiller with XP10 was estimated under representative scenarios and compared to total equivalent warming impact with HFC-134a. Use of XP10 could significantly reduce chiller global warming impact relative to HFC-134a, when chiller refrigerant losses are unavoidably high or when electricity is generated with low GHG emissions. XP10 has the potential to be a more environmentally sustainable future option for medium-pressure centrifugal chillers. [ABSTRACT FROM AUTHOR]

2,3,3,3-Tetrafluoropropene (HFO-1234yf) is being developed as a refrigerant because it has a very low global warming potential (less than 10), as contrasted to the hydrofluorocarbons, which is intended to replace with values of over 500. Several toxicology studies were conducted to develop a toxicology profile for this material. There was no lethality in mice and rats receiving single 4-hour exposures up to 101 850 or 405 800 ppm, respectively. Additionally, there was no mortality or clinical signs of toxicity when rabbits were exposed to 100 000 ppm for 1 hour. Exposures up to 120 000 ppm did not induce cardiac sensitization to adrenalin in dogs. Rats were exposed to HFO-1234yf at levels of 5000, 20 000 and 50 000 ppm 6 hours/day 5 days/week for 2 weeks and at levels of 5000, 15 000 and 50 000 ppm for 4 weeks and for 90 days. No treatment-related adverse effects were noted in these studies. HFO-1234yf was not genotoxic in a mouse and a rat micronucleus assay, and unscheduled DNA synthesis assay and was not clastogenic in human lymphocytes. HFO-1234yf was mutagenic to Salmonella typhimurium TA 100 and Escherichia coli (WP2 uvrA) at concentrations of 20% and higher in the presence of metabolic activation only. There were no biologically significant effects in a rat developmental toxicity study with exposures up to 50 000 ppm. [ABSTRACT FROM AUTHOR]

The regeneration and adsorption of desiccant wheel for producing the dry air was experimentally investigated. The air needed for regeneration was heated in an evacuated tube solar collector with surface area 4.44 m2. The desiccant wheel is regenerated at the temperature in the range of 43.9–72.6°C. The regeneration and adsorption performances are affected by the regeneration temperature, wheel rotation, air flow rate (process and regeneration) and ambient conditions. By comparing the adsorption and regeneration performance at different air flow rate and constant rph, it was found that maximum adsorption and regeneration rates are obtained at air flow rate of 210.789 kg/h. Regeneration temperature directly affects the effectiveness of the desiccant wheel. Maximum desiccant wheel effectiveness of regeneration sector and adsorption sector is obtained at air flow rate of 105.394 kg/h. The regeneration performance of desiccant wheel with evacuated tube solar air collector is suitable for the Indian climate. [ABSTRACT FROM AUTHOR]

This article is an introduction to low global warming potential refrigerants, particularly halogenated olefins and, more specifically, fluorinated propene isomers. A summary of fluorinated propene isomer-based blends (AC-1, DP-1, Fluid H, and JDH) that were investigated as part of the Society of Automotive Engineer's cooperative research programs (CRP150) is provided. These blends were designed to possess global warming potential values less than 150 in order to meet the European Union's Mobile Directive; however, they were later abandoned because some of the blend components demonstrated concerns related to toxicity, ozone depletion potential, and/or reactivity. After the abandonment of these blends, a cooperative research program (CRP1234) was initiated by the Society of Automotive Engineers to focus its development efforts on R-1234yf. In addition to R-1234yf, a few other olefins are being investigated as potential refrigerants by the HVAC&R industry, as indicated by the level of patent activity. To demonstrate the performance potentials of some of these blends, simulations are conducted for several fluorinated propene isomer-based blends for typical unitary AC and refrigeration applications. In addition to these simulations, some of the advantages and disadvantages of fluorinated propene isomers are discussed. [ABSTRACT FROM AUTHOR]

HFO-1234ze is being developed as a refrigerant, propellant, and foam-blowing agent because it has a very low global warming potential (less than 10), as contrasted to the hydrofluorocarbons with values of over 500. Several toxicology studies were conducted to develop a toxicology profile for this material. There was no lethality in mice and rats receiving single 4-hour exposures up to 103,300 or 207,000 ppm, respectively. Exposures up to 120,000 ppm did not induce cardiac sensitization to adrenalin. Rats were exposed to HFO-1234ze at levels of 5,000, 20,000, and 50,000 ppm 6 hours/day 5 days/week for 2 weeks. Predominate findings of increased liver and kidney weights and histopathological changes in the liver and heart suggested that these organs were the targets for HFO-1234ze toxicity. In a 4-week study at 1000, 5000, 10,000, and 15,000 ppm, the only organ showing treatment-related effects was the heart. In a 90-day study with exposures of 1500, 5000, and 15,000 ppm 6 hours/day 5 days/week, again, the heart was the only target organ. The findings consisted of focal and multifocal mononuclear cell infiltrates in the heart. There was no evidence of fibrosis, and, when compared to the 2- and 4-week studies, there did not appear to be an increase in severity with length of exposure. HFO-1234ze was inactive in a mouse and rat micronucleus assay, an Ames assay, and an unscheduled DNA synthesis assay and was not clastogenic in human lymphocytes. It was also not a developmental toxin in either the rat or rabbit, even at exposure levels up to 15,000 ppm. [ABSTRACT FROM AUTHOR]

In preparing inventories of ozone-depleting substance (ODS) substitutes, primarily hydrofluorocarbons, the US employs models consistent with Tier 2 methodologies from the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. The model calculates chemical consumption and emissions for 60 sub-applications, which are aggregated to five application levels. So-called “bottom-up” models require data and assumptions regarding the sub-application industries, including number of products introduced and retired each year, the type and amount of chemicals initially used, the emission pattern of the chemicals and if any released chemical is replaced. Once developed, the bottom-up model's estimates of chemical demand can be compared to “top-down” chemical consumption or sales. Combining these types of data gives a partial picture of the amount of ODS and substitutes introduced to the US economy. This paper examines the top-down data in comparison to the bottom-up estimates derived from the inventory models and discusses possible explanations for the differences noted. [ABSTRACT FROM AUTHOR]

A heat pump cycle using hydrofluorocarbon (HFC125)/hydrocarbon (HC) mixtures [including HFC125/HC290 (M1), HFC125/HC600 (M2), HFC125/HC600a (M3) and HFC125/HC1270 (M4)], working both as water chiller and heat pump water heater, was studied based on fixed minimum heat transfer temperature difference between the refrigerant and the secondary fluid. The coefficient of performance and other parameters including volumetric heating/cooling capacity and exergy efficiency of the system were analysed over the full range of HFC125 composition and compared with that of systems using hydrochlorofluorocarbon (HCFC22) and HFC134a. The results show that, at certain HFC125 concentrations, the HFC125/HC mixtures exhibit better performance and can be used as promising alternative refrigerants to HCFC22 and HFC134a. The results may offer an energy efficient way to simultaneously provide heating and cooling in its present or future applications. [ABSTRACT FROM AUTHOR]

An investigation on flow boiling heat transfer and pressure drop of HFC-134a inside a vertical helically coiled concentric tube-in-tube heat exchanger has been experimentally carried out. The test section is a six-turn helically coiled tube with 5.786-m length, in which refrigerant HFC-134a flowing inside the inner tube is heated by the water flowing in the annulus. The diameter and the pitch of the coil are 305 mm and 45 mm, respectively. The outer diameter of the inner tube and its thickness are respectively 9.52 and 0.62 mm. The inner diameter of the outer tube is 29 mm. The average vapor qualities in test section were varied from 0.1 to 0.8. The tests were conducted with three different mass velocities of 112, 132, and 152 kg/m2-s. Analysis of obtained data showed that increasing of both the vapor qualities and the mass fluxes leads to higher heat transfer coefficients and pressure drops. Also, it was observed that the heat transfer coefficient is enhanced and also the pressure drop is increased when a helically coiled tube is used instead of a straight tube. Based on the present experimental results, a correlation was developed to predict the flow boiling heat transfer coefficient in vertical helically coiled tubes. [ABSTRACT FROM AUTHOR]

Experimental investigation on flow boiling heat transfer characteristics of R404A (R125/R143a/R134a) was carried in a smooth horizontal tube of 7.49-mm inner diameter. The tested conditions were similar to those present in the evaporator of supermarket display cases, refrigerated cabinets, laboratory freezers, etc. The heat transfer coefficients along the length of the test section were experimentally measured under varied heat flux conditions between 4 and 19 kW m-2, mass flow rate between 2.5 and 4.5 g s-1 (57 to 102 kg m-2 s-1), and working pressure between 4.4 and 6.1 bar. The flow patterns for the tested conditions were stratified, stratified-wavy, and near-annular flows, which were confirmed using the Kattan-Thome-Favrat flow pattern maps. The experiments revealed that under the aforementioned operating condition, the nucleate boiling mechanism was predominant in the heat transfer coefficient. Further, unlike high mass flow rate conditions, the presence of nucleation was witnessed even at higher vapor qualities. [ABSTRACT FROM AUTHOR]

Laser diffraction (LD) has been used to measure the particle size of pharmaceutical aerosols. In this study, the application of LD for measuring the particle size of a model suspension metered dose inhaler (MDI) containing a hydrofluorocarbon propellant was investigated using a Sympatec LD apparatus with an automatic spray device. In order to obtain meaningful results, test parameters such as spray distance and temperature needed to be optimized for this model formulation and then well-controlled during testing. Using a suitable LD test methodology, it was found that particle size variations as a function of nonvolatile excipient levels as well as changes to the suspended drug substance could be observed and, in some cases, correlated to cascade impaction results. Based on these studies, it is believed that the methodology is a valuable rapid screening tool for investigating variations in or permutations to suspension MDI formulations. Nonetheless, the trends in the LD droplet size are complicated by the presence of drug-free droplets. Consequently, the results are not always consistent with other particle sizing techniques such as cascade impaction in which the droplets associated with drug are evaluated. Therefore, for suspension MDIs, the ''in-flight'' LD method would probably best be utilized as a complementary sizing technique during formulation development. [ABSTRACT FROM AUTHOR]

This study evaluates the feasibility and coefficient of performance of a domestic dehumidifier when its refrigerant is changed from R-134a to R-600a/R-290 mixed refrigerant (50:50 by mass). Without changing any dehumidifier components, experimental results demonstrate that superior performance characteristics can be achieved with 67.5 g of HC refrigerant, which is only 50% of the original mass of the R-134a refrigerant. Generally, the refrigerant in domestic dehumidifiers can be changed from R-134a to a R-600a/R-290 refrigerant mixture, and the ozone depletion potential and global warming potential are negligible when compared with those of the R-134a refrigerant. [ABSTRACT FROM AUTHOR]

Many of the most cost-effective options for reducing emissions of hydrofluorocarbons (HFCs) involve: reducing leaks; responsible handling practices; replacement with a substance with little or no global warming potential; or reducing the amount of the greenhouse gas (GHG) needed. Some of these options can be implemented immediately for quick emission reductions. However, because many of the types of equipment that rely on these gases have lifetimes ranging from 10 to 30 years, fully implementing these emission reductions can take decades. Reductions in HFC consumption, however, can generally be seen more immediately. Recent US proposals for climate legislation have considered limits on HFC consumption under a cap separate from other GHGs. Whether and how such a cap would be implemented, and the economic efficiencies of such a framework, are the subject of considerable debate. Marginal abatement cost curves developed by the US Environmental Protection Agency are used here to examine possible reductions in HFC consumption, and their associated costs, against targets as envisioned in four proposals for US climate legislation. It is seen that such comparisons depend integrally on how the future growth of HFC consumption is projected; that is, what assumptions underlie the baseline. Furthermore, while it is determined that known options may not be available today to meet the policy proposals examined, current developments in the HFC market, along with the history of those markets in the ozone-depleting substances phaseout, provide indications that deeper reductions are achievable. [ABSTRACT FROM AUTHOR]

Hydrofluorocarbons (HFCs) are greenhouse gases with high global warming potentials that are mainly used in refrigeration and air conditioning. Historically, they were emitted only slowly from such systems and long term containment remains an important engineering and environmental issue. As part of their commitment under the Rio convention, nations are required to report annual calculated production and emissions of all greenhouse gases and the reports submitted by the European countries have been examined to determine the extent to which containment of HFCs (expressed as the rate of emission from the bank remaining in equipment) has changed with time. Although there is wide variation between countries, the annual emission rates of HFCs have improved significantly over the past 10 years and now represent between 5 and 10% of the bank still contained in equipment. This implies that, at the present state of technology, it would take at least 10-20 years for the original mass of refrigerant charged into a system to be released into the atmosphere. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) is one candidate for alternatives to hydrofluorocarbon refrigerants for refrigeration or heat-pump cycles. Since the inherent COP of an air-cooled CO2 cycle is lower than that of HFCs, the use of an expander as an expansion device is recommended to improve the cycle performance of the CO2 cycle. The performance of the expander greatly influences the improvement of the cycle performance. Moreover, an expansion process is complicated, since the expansion process occurring in the expander operated under a typical condition proceeds from supercritical to subcritical. Therefore, it is important to clarify both the expander performance and the expansion process in the expander. In this study, a small vane-type expander is developed, and the performance of the expander is measured. The prototype vane expander has a large leakage loss, and the performance is improved by changing the way of supplying a vane back pressure. Additionally, the expansion process in the expander is examined experimentally and analytically. The transcritical expansion process is also investigated in detail by using a simple piston-cylinder expansion mechanism with a glass window. It is shown that an inflection point of the pressure change under the transcritical expansion process appears with a certain time delay in comparison with an ideal case when the inlet temperature is less than about 40°C. A cluster structure of a CO2 molecule remains for a long time after entering the subcritical region. [ABSTRACT FROM AUTHOR]

The thermal decompositions of 1,1,1-trifluoroethane (CH3CF3) and pentafluoroethane (CHF2CF3) were studied by using a turbulent flow reactor at atmospheric pressure over the temperature ranges of 1213-1333 K and 1273-1373 K. The rate coefficients for these thermal decompositions were determined from the first-order decays of the reactants to be k(CH3CF3) = 1012.9±1.2 exp[-(276 ± 29) kJ s mol-1/RT] and k(CHF2CF3) = 1013.9±1.4 exp [-(324 ± 36) kJ s mol-1/RT]s-1. To examine the reaction paths, we identified the decomposition products using gas chromatography-mass spectrometry (GC-MS) and performed ab initio MO calculations. These results showed that the sequential HF elimination reactions, CH3CF3 → CH2CF2 + HFand CH2CF2 → CHCF + HF, were favorable for the CH3CF3 pyrolysis. On the other hand, four initial steps: CHF2CF3 → CF3CF + HF, CHF2CF3 → CF2CF2 + HF, CHF2CF3 → CHF3 + CF2 and CHF2CF3 → CHF2 + CF3, were possible for the CHF2CF3 pyrolysis. Such a difference in the reaction paths between the CH3CF3, and CHF2CF3 pyrolyses can be explained by fluorine hyperconjugation and by repulsion between the fluorine atoms on the 1- and 2-carbons of each hydrofluoroethane. [ABSTRACT FROM AUTHOR]

Improved monitoring of non-CO2 greenhouse gases in air samples is presented, achieved using a new analytical system based on preconcentration, gas-chromatography and mass spectrometry. In addition to the major HFCs, HCFCs and CFCs, the new observations include the first in situ time series of the C1–C3 PFCs (CF4, C2F6 and C3F8) and the more volatile of the HFCs (CHF3, CH2F2, CH3CF3) alongside SF6, all of which are now monitored routinely as part of the Advanced Global Atmospheric Gases Experiment (AGAGE). Observed trends in newly monitored species are shown, obtained from 1–2 years continuous in situ air analyses at remote monitoring sites at Mace Head (Ireland) and Cape Grim (Australia). Observed deviations in the air background for these gas species are linked to modelled trajectories of air masses arriving at the monitoring stations to indicate potential source regions for emissions in Europe and Australia. In addition, preliminary estimates of 2004 mixing ratio growth rates of compounds are deduced from the observations, which highlight the importance of continuous atmospheric monitoring for verification of consumption-based emission estimates of non-CO2 greenhouse gases. [ABSTRACT FROM AUTHOR]

The acute, subchronic, and developmental and genetic toxicity of hydrofluorocarbon (HFC)-236fa and HFC-236ea were evaluated to assist in establishing proper handling guidance. In acute inhalation studies, rats were exposed whole body for 4 hours to various concentrations of each isomer. Based on the lack of mortality, the approximate lethal concentration for HFC-236ea for male rats was > 85,000 ppm. For HFC-236fa, the LC50 for males and females (combined) was > 457,000 ppm. Narcotic-like effects, e.g., prostration, incoordination, and reduced motor activity, were observed only during exposure to either isomer, but were not evident after termination of exposure. In cardiac sensitization studies, HFC236ea induced cardiac sensitization at 35,000 ppm, with fatal responses occurring at 50,000 ppm and greater. For HFC-236fa, a cardiac sensitization response was observed at 150,000 ppm and greater but not at 100,000 ppm. A fatal cardiac sensitization response was observed in one dog exposed to 150,000 ppm HFC236fa. In 90-day subchronic inhalation studies, male and female rats were exposed whole body to HFC-236ea at concentrations of 0, 5000, 20,000, or 50,000 ppm for 6 hours/day, 5 days/week. Similarly, male and female rats were exposed whole body to HFC-236fa at concentrations of 0, 5000, 20,000, or 50,000 ppm for 6 hours/day, 5 days/week. During exposure, narcotic-like effect (reduced acoustic startle response) was observed at 50,000 ppm with both isomers, although there appeared to be an adaptive response to this effect as the study progressed. With HFC-236ea, dilatation of the seminiferous tubules, without effects on germ or Sertoli cells, was observed only in rats at 50,000 ppm. No other effects on in-life measures or on clinical or anatomic pathology, including histopathology, were observed for either isomer. In rat developmental toxicity studies, no evidence of embryotoxicity or teratogenicity was observed with either isomer exposed up to 50,000 ppm during gestational days 7 to 16. Also, no developmental toxicity was observed in rabbits exposed to HFC-236fa at concentrations of up to 50,000 ppm during gestational days 7 to 19. Neither of the HFC-236 isomers was mutagenic in the Ames reverse mutation assay or clastogenic in the chromosomal aberration assay with human lymphocytes. No increase in chromosomal aberrations was observed in in vivo micronucleus studies with either isomer. [ABSTRACT FROM AUTHOR]

The author reflects on the effect of refrigerants on energy and environment in the U.S. He mentions the challenges involving energy, environment and sustainability in the country. He believes that these problems will raise central societal transformations which affect the way people live, work and play. An overview of the restrictive aspect on hydrofluorocarbons (HFCs) is also presented.